just went to santize the water tank on my pop up and after filling it up all the way it started leaking from the top of the water tank where it is resting on the support rails. it's coming down from the front and rear of the tank. and since the pop up is parked in front of the house on the street its draining to the curb side.

do you think the tank might have a crack? or could there be a vent somewhere?

My fresh water tanks have vents on the top, one per (just looks like a 90deg. elbow fitting). If your tank came like mine, there was no vent tube attached to the actual vent of the tank. Once the tanks were full, water would come out of these vents if I continued to add water.